diff --git a/src/css/base.css b/src/css/base.css
index d0fdaaec..9838b622 100644
--- a/src/css/base.css
+++ b/src/css/base.css
@@ -22,6 +22,7 @@ body {
   font-family: var(--body-font-family);
   line-height: var(--body-line-height);
   margin: 0;
+  tab-size: 4;
   word-wrap: anywhere; /* aka overflow-wrap; used when hyphens are disabled or aren't sufficient */
 }
 
diff --git a/src/css/vendor/asciidoctor-tabs.css b/src/css/vendor/asciidoctor-tabs.css
index 8044104a..920001d8 100644
--- a/src/css/vendor/asciidoctor-tabs.css
+++ b/src/css/vendor/asciidoctor-tabs.css
@@ -44,12 +44,12 @@
   content: none;
 }
 
+.doc .tabs:not(.is-loading) .tablist > ul li {
+  transition: background-color 200ms ease-in-out, color 100ms linear;
+}
+
 .doc .tabpanel {
   background-color: initial;
   border: 0;
   padding: 0;
 }
-
-html.theme-set .doc .tabs .tablist > ul li {
-  transition: background-color 200ms ease-in-out, color 100ms linear;
-}
diff --git a/src/js/07-switch-theme.js b/src/js/07-switch-theme.js
new file mode 100644
index 00000000..9547aa2d
--- /dev/null
+++ b/src/js/07-switch-theme.js
@@ -0,0 +1,35 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the 'License');
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an 'AS IS' BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+;(function () {
+  'use strict'
+
+  activateSwitch(document.getElementById('switch-theme-checkbox'))
+
+  function activateSwitch (control) {
+    if (!control) return
+    control.checked = document.documentElement.classList.contains('dark-theme')
+    control.addEventListener('change', onThemeChange.bind(control))
+  }
+
+  function onThemeChange () {
+    document.documentElement.classList.toggle('dark-theme', this.checked)
+    saveTheme(this.checked ? 'dark' : 'light')
+  }
+
+  function saveTheme (theme) {
+    window.localStorage && window.localStorage.setItem('theme', theme)
+  }
+})()
diff --git a/src/js/vendor/switchtheme.js b/src/js/vendor/switchtheme.js
deleted file mode 100644
index 7846c94c..00000000
--- a/src/js/vendor/switchtheme.js
+++ /dev/null
@@ -1,61 +0,0 @@
-/*
- * Copyright 2021 the original author or authors.
- *
- * Licensed under the Apache License, Version 2.0 (the 'License');
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an 'AS IS' BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-;(function () {
-  'use strict'
-
-  const localStorage = window.localStorage
-  const htmlElement = document.documentElement
-  const prefersDarkColorScheme = window.matchMedia('(prefers-color-scheme: dark)')
-
-  swithInitialTheme()
-  window.addEventListener('load', onWindowLoad)
-
-  function swithInitialTheme () {
-    if (isInitialThemeDark()) htmlElement.classList.add('dark-theme')
-    window.requestAnimationFrame(function () {
-      htmlElement.classList.add('theme-set')
-    })
-  }
-
-  function onWindowLoad () {
-    const toggleCheckboxElement = document.querySelector('#switch-theme-checkbox')
-    toggleCheckboxElement.checked = isInitialThemeDark()
-    toggleCheckboxElement.addEventListener('change', onThemeChange.bind(toggleCheckboxElement))
-  }
-
-  function isInitialThemeDark () {
-    const theme = loadTheme()
-    return theme ? theme === 'dark' : prefersDarkColorScheme.matches
-  }
-
-  function onThemeChange () {
-    if (this.checked) {
-      htmlElement.classList.add('dark-theme')
-      saveTheme('dark')
-    } else {
-      htmlElement.classList.remove('dark-theme')
-      saveTheme('light')
-    }
-  }
-
-  function saveTheme (theme) {
-    if (localStorage) localStorage.setItem('theme', theme)
-  }
-
-  function loadTheme () {
-    if (localStorage != null) return localStorage.getItem('theme')
-  }
-})()
diff --git a/src/partials/footer-scripts.hbs b/src/partials/footer-scripts.hbs
index 16ba1905..4403bdaf 100644
--- a/src/partials/footer-scripts.hbs
+++ b/src/partials/footer-scripts.hbs
@@ -1,7 +1,6 @@
 <script id="site-script" src="{{{uiRootPath}}}/js/site.js" data-ui-root-path="{{{uiRootPath}}}"></script>
 <script async src="{{{uiRootPath}}}/js/vendor/highlight.js"></script>
 <script async src="{{{uiRootPath}}}/js/vendor/{{#if (asciidocExtensionRegistered '@asciidoctor/tabs')}}asciidoctor{{else}}spring{{/if}}-tabs.js"></script>
-<script src="{{{uiRootPath}}}/js/vendor/switchtheme.js"></script>
 {{#if env.ALGOLIA_API_KEY}}
 <script async id="search-script" src="{{{uiRootPath}}}/js/vendor/docsearch.js"{{#if env.ALGOLIA_APP_ID}} data-app-id="{{env.ALGOLIA_APP_ID}}"{{/if}} data-api-key="{{env.ALGOLIA_API_KEY}}" data-index-name="{{env.ALGOLIA_INDEX_NAME}}" data-input-selector="#search-input"></script>
 {{/if}}
diff --git a/src/partials/head-styles.hbs b/src/partials/head-styles.hbs
index 44c9562d..5dabc0bd 100644
--- a/src/partials/head-styles.hbs
+++ b/src/partials/head-styles.hbs
@@ -1,3 +1,8 @@
+    <script>
+!function (theme) {
+  if (theme === 'dark') document.documentElement.classList.add('dark-theme')
+}(localStorage && localStorage.getItem('theme') || (matchMedia('(prefers-color-scheme: dark)') && 'dark'))
+    </script>
     <link rel="stylesheet" href="{{{uiRootPath}}}/css/site.css">
     <link rel="stylesheet" href="{{{uiRootPath}}}/css/vendor/{{#if (asciidocExtensionRegistered '@asciidoctor/tabs')}}asciidoctor{{else}}spring{{/if}}-tabs.css">
     <link rel="stylesheet" href="{{{uiRootPath}}}/css/vendor/docsearch.css">